Among the various flat panel displays, the TFT LCD is dominating the flat panel display market because of lower power consumption, relatively low manufacturing cost, and substantial no radiation. The TFT LCD device is formed by assembling an array substrate and a color filter substrate with a liquid crystal layer interposed therebetween.
FIG. 1A is a top plan view of a single pixel of a conventional amorphous silicon TFT LCD array substrate, and FIGS. 1B and 1C are cross-sectional views taken along the line A-A and line B-B of FIG. 1A, respectively. The array substrate comprises a plurality of gate lines 1 and a plurality of data lines 5 perpendicular to the gate lines 1. The adjacent gate lines and data lines define a plurality of pixel areas. Each pixel area comprises a TFT switching device, a transparent pixel electrode 10, and optionally a common electrode 11. The TFT device is configured as a bottom gate type by a back channel etching as shown in FIG. 1B. The TFT switching device comprises a gate electrode 2, a gate insulating layer 4, a semiconducting active layer 3, a source electrode 6, and a drain electrode 7. A passivation layer 8 is coated over the above-mentioned components, and a passivation layer via hole 9 is formed above the drain electrode 7. The transparent electrode 10 is connected with the drain electrode 7 of the TFT device via the passivation layer via hole 9. The source electrode 6 is connected with one of the data lines 5. A storage capacitor 13 is formed by overlapping the pixel electrode 10 with the gate line 1 and overlapping the pixel electrode 10 with the common electrode 11. In order to lower and reduce the light leakage within pixel after assembling the substrates, light blocking bars 12 are formed on the sides, which are parallel to the data lines, of the pixel electrode 10, which configuration can reduce the light induced current leakage in the channel of the TFT device. The light blocking bars 12 can be made of the same material as the gate electrode 2 in a same mask photolithography) process. The common electrode 11 can also be made of the same material as the gate electrode 2 and is connected with the light blocking bars 12, as shown in FIGS. 1A and 1C.
The five-mask (photolithography) process is a typical manufacturing technology for a TFT LCD array substrate at present and generally comprises the following five steps:
1). forming a gate electrode and gate line, and optionally forming light blocking bars and/or common electrodes simultaneously;
2). forming a gate insulating layer and an active layer;
3). forming a source electrode, a drain electrode, and a data line;
4). forming a passivation layer; and
5). forming a pixel electrode.
Each of the steps comprises three main processes, namely, thin film deposition, forming of the etching mask pattern (coating a photoresist layer, exposing with a mask plate, and developing), and etching. Each of the five steps uses a mask plate to pattern the respective deposited layer. The above process is typical for the 5-Mask technology. Other 5-Mask technologies could also be employed by changing the mask plate design and the process flow.
In the TFT LCD array substrate as shown in FIG. 1A, since the common electrode structure (including the light blocking bars 12 and common electrode 11) is formed in an “H” shape in the central portion of the pixel area, the aperture ratio is decreased. The “H” shape structure also needs new manufacturing process and repairing method. In the conventional TFT LCD array substrate, the capacitance occurring between the common electrode 11 and the data line 5 can also affect the data transmission through the data line 5. A schematic view of the load current for the common electrode of the conventional TFT LCD is shown in FIG. 2, in which the current is mainly concentrated in the horizontal direction, for which the conventional solutions are to improve the peripheral circuit design and improve the way of inputting signals.